This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Rab5 is a signaling protein that exists in three isoforms. All forms (Rab5 A, Rab5B, Rab5 C) have significant sequence homology and similar structures. It was once believed that these proteins were redundant, however recent studies with knock out mice have demonstrated that each isoform is required healthy animals. A conformational change occurs upon binding GDP or GTP.